Fig. 1. (a) The PMMA layer is deposited on a 70-nm-thick gold film, forming a circular shape. (b) The PMMA layer is drilled to generate nanometer-sized cylindrical holes.

Fig. 2. (a) The variation of effective refractive index at the center of the lens for different values of F. (b) The variation of central radius for both configurations with different values of F. The smallest radius is 25 nm.

Fig. 3. (a) The 12-fold symmetry design and (b) the square lattice design.

Fig. 4. Electric field profiles of SPPs propagating through metasurfaces with a 12-fold symmetry design and a square lattice design.

Fig. 5. Field intensities along the z-axis for metasurfaces with (a) 12-fold symmetry and (b) square lattice designs. Field intensities for both designs are calculated on the x–z plane; refer to (e) and (f) for visualization. (c) Comparison of field intensities for a continuous Luneburg lens and Luneburg lenses with square lattice and 12-fold symmetry designs. (d) Comparison of field intensities for a continuous Luneburg lens cut at ρ = 4.35 µm and Luneburg lenses with a square lattice design. FWHM measurement at the focal plane for a Gutman lens (F = R_L) (g) with a square lattice design and (h) without GRIN.